test

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication16
{
    class Program
    {
        static void Main(string[] args)
        {
            var collection = new List<int>
            {
                5, 6, 7, 8, 9, 10
            };

            Test(collection);

            foreach(var value in collection)
            {
                Console.WriteLine(value);
            }

            var result = new List<int>
            {
                5, 6, 7, 8, 9, 10
            };

            try
            {
                Test(ref result);

                foreach (var value in result)
                {
                    Console.WriteLine(value);
                }
            } catch(Exception ex)
            {
                Console.WriteLine(ex.Message);
            }
        }

        static void Test(List<int> collection)
        {
            collection = null;
        }

        static void Test(ref List<int> collection)
        {
            collection = null;
        }
    }
}